AALSMA, Lars | University of Wisconsin-Madison | Title: Nothing Lasts... But Nothing Is Lost in de Sitter Space Abstract: In a spacetime with a horizon, information can be classically lost to an observer when it falls behind the horizon. However, quantum mechanically horizons emit Hawking radiation and unitary evolution suggests that this radiation captures information from behind the horizon. Recent works have revealed how these two seemingly conflicting point of views can be made compatible by taking into account a newly discovered saddle point in the gravitational path integral. In this talk, I will apply these ideas to de Sitter space and argue that, just as for black holes, no information can be lost in de Sitter space. However, the price of an observer’s curiosity comes at price as it induces large backreaction. |

ALLALI, Itamar | Tufts University | Title: Gravitational Decoherence with Applications to Dark Matter Phenomenology Abstract: Nontrivial quantum arrangements of matter, such as Schrodinger cat-like states, are sensitive to decoherence from their environment. However, matter that interacts only gravitationally is weakly coupled to its environment, and thus may exhibit slower rates of decoherence. Since dark matter (DM) may only interact via gravity, we explore the decoherence rate of a dark-matter-Schrodinger-cat-state (DMSCS). In the nonrelativistic approximation of gravity, we find that a superposition of distinct DM density profiles can undergo decoherence from the scattering of nearby standard model (SM) particles on observable timescales. In addition, when considering light bosonic DM like an axion, one can conceive of a superposition of the phase of oscillation of the scalar (axion) field, requiring a truly relativistic formalism of gravitational scattering. We derive such a formalism and find that for typical DM populations in the Milky Way, a DMSCS of the axion phase can maintain quantum coherence for exponentially long times, while exotic configurations including DM near a black hole and dense boson stars can experience rapid decoherence. This can have potential observable consequences for direct detection experiments that are sensitive to the axion’s phase, such as haloscopes which rely on resonant cavities to detect axions. This talk will be based on the work in Refs. 2005.12287, 2012.12903, and 2103.15892. |

BITAGHSIR FADAFAN, Kazem | Shahrood U. of Technology | Title: Magnetically-Induced Holographic Composite Inflation Abstract: We study the observational predictions of the phenomenological AdS/QCD inspired model, in which the inflaton field emerges in a four dimensional strongly coupled gauge theory, in which the chiral symmetry breaking occurs through the formation of quark condensate. Based on a top-down approach of AdS/QCD, using a D7 brane in the background of Nc D3 branes, it has already been shown that chiral symmetry breaking in a magnetic field through the generation of Higgs vacuum expectation value could be a second order phase transition, although it was doubted that this scenario could lead to enough amount of inflation. Using an iterative method, we consistently solve for the time-dependent parameters, including the embedding function of the D7 brane and the Hubble parameter of the expanding background. We show that the predictions of the inflationary model is consistent with the most stringent constraints placed on the inflationary models by Planck 2018. Although the model is capable of producing a large amount of gravitational waves, r≃0.01, the displacement of the canonical mass dimension one scalar field remains below the Planck mass, in violation of the Lyth bound. |

CAHILL, Kevin | University of New Mexico | Title: Is the local Lorentz invariance of general relativity implemented by gauge bosons that have their own Yang-Mills-like action? Abstract: General relativity with fermions has two independent symmetries: general coordinate invariance and local Lorentz invariance. General coordinate invariance is implemented by the Levi-Civita connection and by Cartan's tetrads both of which have as their action the Einstein-Hilbert action. It is suggested here that local Lorentz invariance is implemented not by a combination of the Levi-Civita connection and Cartan's tetrads known as the spin connection, but by independent Lorentz bosons $L^{ab}_{ph{ab} i}$ that gauge the Lorentz group, that couple to fermions like Yang-Mills fields, and that have their own Yang-Mills-like action. Because the Lorentz bosons couple to fermion number and not to mass, they generate a static potential that violates the weak equivalence principle. If a Higgs mechanism makes them massive, then the static potential also violates the inverse-square law. Experiments put upper bounds on the strength of such a potential for masses $m_L < 20$ eV. These upper limits imply that Lorentz bosons, if they exist, are nearly stable and contribute to dark matter. |

CHAKRABORTY, Dibya | University of Guanajuato |
Title: Moduli Stabilisation on the Conifold: a New de Sitter Solution In this talk, I will address the challenges of obtaining a dS vacua in type IIB flux compactifications that include a warped throat region of Klebanov-Strassler type corresponding to a warped deformed conifold, with an anti-D3-brane sitting at its tip. Previous studies have shown that the dS uplift in the KKLT type scenario in the strongly warped regime where the warping introduces a coupling between the conifold’s deformation modulus and the bulk modulus, may destabilise the closed string moduli, unless the tadpole bound is compromised. However, we explore a new regime where the warping term is subdominant. We thus discover a new metastable de Sitter solution within the four-dimensional effective field theory, with full moduli stabilisation using Large Volume Scenario. We discuss the position of this de Sitter vacuum in the string theory landscape. |

CHOI, Kang Sin | Ewha Womans University | Title: Aligned Natural Inflation in the not-so-Large Volume Scenario. Abstract: Natural inflation identifies an axion as an inflaton. Although it solves flat potential (eta) problem, it suffers naturalness problem since the current observation requires the trans-Planckian decay constant. We show that embedding it to string theory, with moduli stabilization by Large Volume Scenario, naturally explains an aligned axion giving a large decay constant. Constraint from weak gravity conjecture puts interesting constraints on the internal geometry, whose Kahler moduli are associated to the axions. |

CHOI, Sunjin | KIAS | Title: The Yang-Mills duals of small AdS black holes Abstract: We study the large N matrix model for the index of 4d maximal super-Yang-Mills theory on S^3 X R and its truncations to understand the BPS black holes in dual AdS_5. Numerical studies of the truncated models provide insights on the black hole physics, some of which we investigate analytically with the full Yang-Mills matrix model. In particular, we find many branches of saddle points which describe the known black hole solutions. We analytically construct the saddle points dual to the small black holes whose sizes are much smaller than the AdS radius. They include the asymptotically flat BMPV black holes embedded in large AdS with novel thermodynamic instabilities. |

CHOUDHURY, Sayantan | National Institute of Science Education and Research, Bhubaneswar. |
Title: Thermalization Phenomena in Quenched Quantum Brownian Motion in De Sitter Space In this article, we study the quantum field theoretic generalization of the Caldeira-Leggett model to describe the Brownian Motion in general curved space-time considering interactions between two scalar fields in a classical gravitational background. The thermalization phenomena is then studied from the obtained de Sitter solution using quantum quench from one scalar field model obtained from path integrated effective action in Euclidean signature. We consider an instantaneous quench in the time-dependent mass protocol of the field of our interest. We find that the dynamics of the field post-quench can be described in terms of the state of the generalized Calabrese-Cardy (gCC) form and computed the different types of two-point correlation functions in this context. We explicitly found the conserved charges of $W_{infty}$ algebra that represents the gCC state after a quench in de Sitter space and found it to be significantly different from the flat space-time results. We extend our study for the different two-point correlation functions not only considering the pre-quench state as the ground state, but also a squeezed state. We found that irrespective of the pre-quench state, the post quench state can be written in terms of the gCC state showing that the subsystem of our interest thermalizes in de Sitter space. Furthermore, we provide a general expression for the two-point correlators and explicitly show the thermalization process by considering a thermal Generalized Gibbs ensemble (GGE). Finally, from the equal time momentum dependent counterpart of the obtained results for the two-point correlators, we have studied the hidden features of the power spectra and studied its consequences for different choices of the quantum initial conditions. |

GHIM, Dongwook | Korea Institute for Advanced Study | Title: 5d BPS quivers and KK towers Abstract: This talk will present recent progress in computing (refined) Witten index of BPS quiver for 5d gauge theories, compactified on a circle. With stringy BPS objects in 5d theory being wrapped on the circle, the wall-crossing problem of 4d KK theory can be addressed by N=4 quiver quantum mechanics. However, the fine-tuned superpotential of the latter makes many of the known machinery fail to capture its Witten indices. I will show how the subtlety can be bypassed for a restricted class of BPS quivers. Specifically, the L2 cohomology counting and D0 brane picture will construct neutral KK sectors. Then I will show how to apply Coulomb branch formula to purely electric BPS sectors. |

HWANG, Chiung | Cambridge University | Title: E-string on Spheres Abstract: We consider compactifications of the 6d rank Q E-string theory on a genus zero surface with flux for various subgroups of the E_8 x SU(2) global symmetry of the E-string theory. The 4d models we propose exhibit interesting IR enhancements of global symmetry as well as duality properties, which can be clearly understood from their 6d origins. Furthermore, we show that those models possess an additional SU(2) symmetry that doesn’t descend from the 6d global symmetry and can be identified with the isometry of the two-sphere. We give evidence for this identification by computing the ’t Hooft anomalies of the SU(2) symmetry in 4d and comparing them with the predicted anomalies from the 6d perspective. |

JEONG, Saebyeok | Rutgers | Title: Defects and quantization Abstract: The correspondence between four-dimensional N=2 supersymmetric field theories and vertex algebras induces many interesting consequences. I will first explain insertion of defects in gauge theory leads to nontrivial results regarding the quantization problem of Hitchin integrable systems and the isomonodromic problem of Fuchsian systems. Then I will discuss how we can connect our 4d N=2 setting to the 4d N=4 setting of Kapustin-Witten, yielding the same two-dimensional sigma model with Hitchin target space under dimensional reduction, especially by giving proper interpretations of the defects in the 4d N=2 side along the connection. The first part is based on several works with Norton Lee and Nikita Nekrasov, and the second part is based on an ongoing work with Nikita Nekrasov. |

KARKHEIRAN, Mohsen | IBS-CTPU | Title: Yukawa couplings of the effective theory from spectral data Abstract: We consider a Heterotic string theory compactified on an elliptically fibered Calabi-Yau threefold with a vector bundle over that defined with some spectral data $(mathcal{L},mathcal{S})$. We will study the Yukawa textures of the effective theory in terms of the geometry of the spectral cover $mathcal{S}$ and possible spectral sheaves $mathcal{L}$ supported on $mathcal{S}$. These results will automatically translate to a local F-theory model. |

KUNG, Yu-Hsien | National Taiwan University | Title: Flow-induced soft hair and the modification to the Hawking temperature Abstract One interesting proposal to solve the black hole information loss paradox without modifying either general relativity or quantum field theory, is the soft hair, a diffeomorphism charge that records the anisotropic radiation in the asymptotic region. This proposal, however, has been challenged, given that away from the source the soft hair behaves as a coordinate transformation that forms an Abelian group, thus unable to store any information. To maintain the spirit of the soft hair but circumvent these obstacles, we consider Hawking radiation as a probe sensitive to the entire history of the black hole evaporation, where the soft hairs on the horizon are induced by the absorption of a null anisotropic flow, generalizing the shockwave considered by Hawking et al. To do so we introduce two different time-dependent extensions of the diffeomorphism associated with the soft hair, where one is the backreaction of the anisotropic null flow, and the other is a coordinate transformation that produces the Unruh effect and a Doppler shift to the Hawking spectrum. Together, they form an exact BMS charge generator on the entire manifold that allows the nonperturbative analysis of the black hole horizon, whose surface gravity, i.e. the Hawking temperature, is found to be modified. The modification depends on an exponential average of the anisotropy of the null flow with a decay rate of 4M, suggesting the emergence of a new 2-D degree of freedom on the horizon, which could be a way out of the information loss paradox. |

LANZA, Stefano | Utrecht | Title: The EFT stringy viewpoint on large distances Abstract: The Swampland distance conjecture predicts that, in any consistent effective field theory of quantum gravity, infinite field distance limits correspond to the breaking of the effective description due to the appearance of infinite towers of massless states. Albeit there are several top-down arguments supporting the conjecture, a proper bottom-up justification is still lacking. In this talk, I will propose a mechanism that realizes the conjecture within any consistent 4D theory. The key objects to introduce are strings that are magnetically coupled to axions. I will illustrate how their backreaction allows one to probe different regions of the field space. Infinite field distance limits are reached when the string becomes tensionless. Furthermore, I will show how, along such limits, an infinite tower of states appears, becoming massless with a rate fixed by the string tension. |

LEE, Kanghoon | APCTP | Title: Berends-Giele recursion relation for gravity Abstract: We construct the all order metric perturbation theory from double field theory. Using this result, we derive a novel off-shell recursion relation for graviton scattering amplitude, which is the gravity counterpart to the Berends-Giele recursion relation for Yang-Mills theory. |

LITTERER, Jacob | Tufts University | Title: Lorentz Invariance from Locality of Massless Spin 2 Abstract: It is known that local, Lorentz invariant, unitary theories involving particles with spin 1 demand that the matter sector they couple to are organized by internal physical symmetries and the associated charge conservation, while spin 3/2 demands supersymmetry. However, the introduction of a spin 2 graviton does not obviously demand new symmetries of the matter sector (although it does demand a universal coupling). In recent work we relaxed the assumption of Lorentz boost symmetry, while maintaining a basic notion of locality that there is no instantaneous signaling at a distance. In order to avoid potential problems with longitudinal modes of the graviton, we chose to project them out, leaving only two degrees of freedom. This nevertheless leaves a large classes of theories that a priori may violate Lorentz boost invariance. By requiring the tree-level exchange action be local, consistency demands that the Lorentz boost symmetry must be satisfied by the graviton and the matter sector, which in turn recovers general relativity uniquely at this order of analysis. In this sense, the Lorentz boost symmetry can be seen to be an underlying physical symmetry that is demanded of the graviton and matter sectors, analogous to internal symmetries of theories involving spin 1, a fact which is usually taken for granted. |

MEHTA, Viraf | University of Goettingen | Title: Landscape Exploration with Black Holes Abstract: We use our unprecedented access to Calabi-Yau geometries derived from the Kreuzer-Skarke database to construct multiaxion potentials with up to 491 axions. We analyse the statistics of a large, representative ensemble of these systems and use properties of black holes to exclude a fraction of the landscape. |

NOUMI, Toshifumi | Kobe University | Title: Gravitational Positivity Bounds and the Standard Model Abstract: We discuss compatibility of the Standard Model of particle physics and gravitational positivity bounds on low-energy scattering amplitudes, which provide a necessary condition for a low-energy gravitational theory to be UV completable within the weakly coupled regime of gravity. In particular, we identify the cutoff scale of the Standard Model coupled to gravity by studying consistency of light-by-light scattering. While the precise value depends on details of the Pomeron effects in QCD, the cutoff scale reads 10^{16} GeV if the single-Pomeron exchange picture works well up to this scale. We also demonstrate that the cutoff scale is lowered to 10^{13} GeV if we consider the electroweak theory without the QCD sector. |

OEHLMANN, Paul-Konstantin | Uppsala | Title: Gauged 2-form symmetries in 6D SCFTs coupled to Gravity Abstract: 6D SCFTs can admit a plethora of global symmetries such as discrete 2-form symmetries that are expected to be either broken or gauged when coupled to gravity. In this talk we discuss the geometric condition on the compactification spaces for (2,0) and (1,0) SUGRA theories coupled to SCFT sectors that admit a gauged 2-form symmetry sub-group. We further test our proposal via various string dualities. |

PAPADIMITRIOU, Ioannis | KIAS | Title: Anomalies and Supersymmetry Abstract: I will discuss the structure of perturbative anomalies of continuous global symmetries in supersymmetric quantum field theories and how this can be determined either using a generalized BRST algebra and anomaly descent procedure, or through supersymmetric anomaly inflow from one dimension higher. I will then explain the implications of such anomalies for the dependence of supersymmetric observables on the moduli of curved backgrounds that admit Killing spinors. |

RAMOS HAMUD, Mario | Institute of Physics, UNAM | Title: The Flavour of String Theory Abstract: With the goal in mind of finding in string theory some guiding principle that singles out the discrete symmetries that might govern the mixing patterns of fermions in the SM, we studied the generalised "Eclectic Flavour Group" which leads to a hybrid picture where the traditional flavour group and the finite modular group combine. In this way, motivated by the origin of both symmetries in string theory, the phenomenology of certain eclectic flavour groups has been analysed in different extensions of the standard model from the bottom-up perspective. |

RIGHI, Nicole | DESY | Title: Fuzzy dark matter candidates from strings Abstract: We provide a string theoretical explanation of Fuzzy Dark Matter as composed by ultra-light axions coming from the compactification of type IIB string theory on Calabi-Yau manifolds. In particular, we consider C4 axions stabilised in a Large Volume Scenario, and axionic modes living in warped throats of the internal manifold. Based on the latest bounds, we study how likely is for dark matter to be composed of such particles and in which abundance. We provide predictions on the preferred ranges of masses and decay constants when string axions behave as FDM. Moreover, requiring those axions to lie in the FDM range imposes constraints on the features of the internal manifold. We also comment on implications for the WGC. Keywords: String, Cosmology |

SCHIMANNEK, Thorsten | University of Vienna | Title: Z_5 Symmetries in F-theory, Homological Projective Duality and Modular Forms Abstract: Genus-one fibered Calabi-Yau manifolds with 5-sections lead to F-theory vacua with Z_5 gauge symmetry. Geometrically, the 5-section case is interesting because the normal form of the fibers is not a complete intersection in a toric ambient space. This turns out to have striking implications for the modular structure of the topological string partition functions. One of the tools in our analysis are elliptic complete intersections in toric ambient spaces that lead to vacua with charge 5 matter in F-theory. Using Higgs transitions, which geometrically correspond to extremal transitions to genus-one fibrations with 5-sections, we discover a beautiful interplay between the modular structure on different genus-one fibrations, the associated physics in M-/F-theory and non-Abelian GLSMs, as well as the arithmetic and algebraic geometry. |

SERRA, Francesco | Scuola Normale Superiore, Pisa | Title: An effective two-body approach to the hierarchical three-body problem in General Relativity Abstract: Gravitationally bound binaries are often orbited by a distant third body, forming a hierarchical three-body system. Over the course of many orbital periods, the perturbation of the third body can excite eccentricity oscillations and orbital flips of the inner binary. In this talk I will discuss how to describe these perturbations alongside relativistic corrections to the Newtonian dynamics, by means of an Effective Field Theory approach. I will show that this makes possible to treat the inner binary as an effective point-particle, mapping the three-body problem to a simpler two-body motion. The evolution of the inner binary over long timescales will thus be encoded in the time dependence of a set of multipole moments. I will argue that this description efficiently captures both the long timescale effects distinctive of the hierarchical three-body problem and the coupling of the system to gravitational radiation. |

SOLER, Pablo | IBS-CTPU | Title: D-brane gaugino actions and their role in moduli stabilization Abstract: Within the ongoing debate about de Sitter (dS) vacua in string theory, different aspects of explicit dS proposals have come under intense scrutiny. One key ingredient is D7-brane gaugino condensation, which can be straightforwardly treated using effective 4d supergravity. However, it is also desirable to derive the relevant scalar potential directly from a 10d Lagrangian. While progress in this endeavour has recently been made, issues related to divergences and non-localities related to the quartic gaugino coupling have remained problematic in the available proposals. I will discuss an explicitly local and finite D7-brane quartic gaugino term which reproduces the relevant part of the 4d supergravity action upon dimensional reduction. This action can then be used to give a 10d description of moduli stabilization. This is both a step towards a more complete understanding of 10d type-IIB supergravity as well as specifically towards better control of dS constructions in string theory involving gaugino condensation. |

SPERLING, Marcus | YMSC, Tsinghua University | Title: Quantum curves for 6d N=(1,0) theories Abstract: The quantisation of the Seiberg-Witten curves of 6d theories compactified on a two-torus leads to difference operators, which are in the class of elliptic quantum curves. In this talk, I will illustrate two examples: firstly, 6d N=(1,0) SU(n) theory with 2n fundamental flavours and, secondly, the 6d E-string theory. For both cases, the quantum curves can be rephrased as eigenvalue equations. The eigenfunctions correspond to codimension 2 defect operators and the eigenvalues are codimension 4 Wilson surfaces wrapping the elliptic curve, respectively. Among others, I will comment on a path-integral derivation of the quantum curve and the relation to integrable models, such as the van Diejen model for the E-string. |

WARKENTIN, Max | LMU Munich | Title: The Casimir effect in the presence of infrared transparency Abstract: I will address the gravitational Casimir effect. Even though the gravitational field interacts very weakly with matter, in the presence of the so-called infrared transparency, a quantized gravitational field would lead to a Casimir force exhibited by two surfaces. Such a phenomenon occurs naturally when a quantum field has localized kinetic terms on a lower dimensional brane, as e.g. in the DGP model. I will show that in that case the branes act as ”effective” boundary conditions for the gravitational field, so that the gravitational Casimir force between them emerges. Since the branes do not provide perfect boundary conditions as in the standard paradigm of conducting plates and the electromagnetic field, the resulting Casimir force deviates from the standard one. |

YOON, Junggi | KIAS | Title: TTbar deformation of 2d N=(1,1) SUSY model and 3D N=2 Green-Schwarz Action Abstract: In this talk, I will discuss the relation between TTbar deformation of 2d N=(1,1) SUSY model and 3D N=2 Green-Schwarz action. First, I will present the Hamiltonian analysis of (non-SUSY) TTbar deformation of free N=(1,1) SUSY model, and I will show the supersymmetry of the deformed model. Then, I will describe how the TTbar deformation is related to N=2 Green-Schwarz action for 3D target space. Finally, I will demonstrate the 3D N=2 SUSY is equivalent to the TTbar deformed N=(1,1) SUSY together with global fermionic symmetry. |